For proper management of patients having severe heart disease, the need for a method of temporary cardiac assist has become increasingly apparent. To date, the methods developed have required the complexities of extracorporeal circulation, insertion of intracorporeal pumps having extracorporeal energy sources, insertion of extracardiac compression devices or have relied upon an indirect approach such as counterpusation. The purpose of this project is to develop and explore the advantages of direct cardiac assist by synchronously inflating and deflating a balloon within the left ventricular cavity. A reproducible model for acute and chronic left ventricular failure in calves will be employed using the technique of microembolization of the coronary arteries. An intraventricular balloon which is inflated during systole with gas will be inserted into the failing heart to maintain peripheral circulation. Controlled experiments will allow evaluation of the effectiveness of the method with respect to maintaining the circulation, maintaining life, allowing myocardial healing, and will assess possible harmful effects on the blood, the endocardium, and the mitral valve. Later, if appropriate, refinements in technique and equipment can be made in order to approach the clinical situation.